A major characteristic of tumor malignancy and the primary cause of morbidity and mortality in patients with breast cancer is the ability of tumors cells to metastasize to distant sites in the body. Therefore, it is important to develop therapeutic strategies for the control and prevention of the metastatic process in order to successfully treat this disease. Our previous work indicates that cyclopropyl antiestrogens are very potent inhibitors of breast tumor cell growth and have the potential to inhibit the growth and metastatic spread of breast cancer. Invasiveness is a fundamental characteristic of metastatic cells. Thus, the major objective of the proposed study is to determine the influence and mechanism of the cyclopropyl antiestrogens on breast cancer cell invasiveness using both ER-positive MCF-7 and ER-negative MDA-MB-231 human breast cancer cells. Invasiveness involves the attachment of tumor cells to the basement membrane, production of proteolytic enzymes for matrix digestion and tumor cell migration. Accordingly, in vitro invasion assay will be used to study the influence of the cyclopropyl antiestrogens on the invasiveness of normal breast, MCF-7 and MDA-MB-231 cells. The influence of the cyclopropyl antiestrogens on actual cell movement, characteristics and kinetics of locomotion will also be determined in normal breast, and breast cancer cell using time-lapse videomicroscopy. The effect of the cyclopropyl antiestrogens on the morphology, ultrastructure and cytoskeleton of these cells will be examined using scanning and transmission electron microscopy. Attachment of the tumor cell to laminin has been shown to initiate a cascade of events involved in the metastatic process. Accordingly, the inhibitory effect of cyclopropyl antiestrogens on the laminin-mediated cellular attachment to the basement membrane will be evaluated in this study. In addition, the effect of cyclopropyl antiestrogens on the release and activity of proteolytic enzymes such as collagenase IV and plasminogen activator, which are also key factors in the metastatic process, will be determined in these cell lines. The results of this study will reveal the antimetastatic activity of cyclopropyl antiestrogens at several major steps along the metastatic cascade, and thus, establish the therapeutic potential of these compounds. Cyclopropyl antiestrogens which display a complete lack of estrogen activity, a very low level of acute toxicity and potent inhibition of breast cancer cell proliferation and metastatic spread should be superior to currently available antiestrogens in the treatment and/or prevention of the metastatic sequelae of breast cancer. Finally, this study will provide important new information on tumor cell locomotion and the relationship between tumor cell morphology and invasiveness.